diff --git a/src/pyrecest/tracking/ellipse_geometry.py b/src/pyrecest/tracking/ellipse_geometry.py
index 12b41bdfb5..163e55f633 100644
--- a/src/pyrecest/tracking/ellipse_geometry.py
+++ b/src/pyrecest/tracking/ellipse_geometry.py
@@ -146,7 +146,7 @@ def wrap_ellipse_angle_to_reference(reference, theta):
 def ellipse_extent_matrix(orientation, semi_axes):
     """Return the SPD extent matrix encoded by ``orientation`` and semi-axes."""
 
-    semi_axes = maximum(asarray(semi_axes).reshape(2), 0.0)
+    semi_axes = backend_abs(asarray(semi_axes).reshape(2))
     rotation = rotation_matrix_2d(orientation)
     return symmetrize(rotation @ diag(semi_axes**2) @ rotation.T)
 
diff --git a/tests/tracking/test_ellipse_extent_negative_axes.py b/tests/tracking/test_ellipse_extent_negative_axes.py
new file mode 100644
index 0000000000..f603891cdb
--- /dev/null
+++ b/tests/tracking/test_ellipse_extent_negative_axes.py
@@ -0,0 +1,25 @@
+from __future__ import annotations
+
+import numpy as np
+import numpy.testing as npt
+
+from pyrecest.tracking import ellipse_extent_matrix, extent_matrix_from_shape
+
+
+def test_extent_matrix_is_invariant_to_axis_sign_representation() -> None:
+    theta = 0.3
+    positive_axes = np.array([3.0, 1.0])
+    signed_axes = np.array([-3.0, -1.0])
+
+    expected = ellipse_extent_matrix(theta, positive_axes)
+
+    npt.assert_allclose(
+        ellipse_extent_matrix(theta, signed_axes),
+        expected,
+        atol=1e-12,
+    )
+    npt.assert_allclose(
+        extent_matrix_from_shape(np.array([theta, *signed_axes])),
+        expected,
+        atol=1e-12,
+    )